C. Loh, M. Newman, D. Zmood and D. Holmes, "A comparative analysis of multiloop voltage regulation strategies for single and three-phase UPS systems", IEEE Transactions on Power Electronics, vol. 18, no. 5, pp. 1176—1185, 2003
J. Guerrero, L. Garcia De Vicuna, J. Matas, M. Castilla and J. Miret, "Output Impedance Design of Parallel-Connected UPS", IEEE Transaction on Industrial Electronics, vol. 52, no. 4, pp. 1126—1135, 2005